Public Warning Systems (PWS,) like for example an earthquake and tsunami warning system (ETWS) or a commercial mobile alert system (CMAS), have been standardized by the Third Generation Partnership Project (3GPP) and have been deployed at several locations around the world. The purpose of a public warning system is to warn people of possible catastrophic situations by alerting mobile devices, for example user equipments like mobile phones, via paging and distributing warning information via for example a system information in Long Term evolution (LTE) systems or via a cell broad-cast (CBS) in Global Systems for Mobile communications (GSM) and Universal Mobile Telecommunication Systems (UMTS). Furthermore, mobile devices in connected mode may be alerted via a dedicated signalling. Examples of such catastrophic situations may be tsunamis, earthquakes, hurricanes and so on.
The public warning systems are designed to effectively reach as much mobile devices as possible within a short period of time, e.g. around a view minutes in total or even only within seconds in the operator network. This may be accomplished by broadcasting warning notifications to multiple mobile devices simultaneously with no requirements on acknowledgement as defined for example in 3GPP TS 22.268.
However, in case of a catastrophic situation, when public warning is issued by the public warning systems, parts of the mobile network may be dysfunctional resulting in a number of mobile devices which are unreachable, as some base stations may have collapsed from physical damage or power shortage from for example an earthquake.
Therefore, there is a need to improve warning people in such situations.